If you get anywhere close with stain removal stop. It is very easy to overdo it and then it looks worse than the original stain. Wipe the whole piece with mineral spirits and you can get an idea of what it will look like finished but the spirits will evaporate quickly and leave you with a clean surface. If you have found varnish on the wood it will need to be stripped completely. If it was only oiled you can build up oil coats to try and match the joint between old and new and then re oil the whole piece.